The present invention relates to a method of treating capillary fibers to be used, for example, in blood dialyzer.
German Pat. No. 864,904 discloses a process for producing capillary fibers by extruding a solution or melt of cellulose, from an orifice of several hundred microns into a coagulating solution. In Japanese Patent Publication No. 50-40168, dated Dec. 22, 1975, and the Technical Information Bulletin No. 12 of Enka Glanz Stoff, AG., Wuppertal, West Germany, dated September, 1976, similar capillary fibers made of polymeric cellulose material, such as cellulose acetate, polyacrylonitrile, polymethyl-methacrylate, and the like, by simultaneously extruding through them an oily substance. The oily substance extruded through the center of the extruded polymeric material forms a hollow center in the polymeric material as it is discharged from the extrusion orifice. It is known to use, as the oily substance, octyl alcohol, isopropyl myristate or the like, which are immiscible with the polymeric material. Then, glycerol is added to the hollow capillary fibers as a softening agent. The capillary fibers, with the softening agent, are dried and thereafter wound on a bobbin to continuously produce a semi-permeable capillary tube having a cross section of a true circle. Blood dialyzer used as artificial kidney or the like is prepared by forming a bundle of a large number of the so produced semipermeable capillary fibers having section of true circle, arranging it within the dialyzer housing made of a plastics such as acrylonitrile-styrene copolymer, acrylic resin, polycarbonate, fixing the both ends of the bundle with an adhesive, and thereafter cutting these ends. The oily substance contained within the capillary fibers is then removed by treating the bundle with ethyl alcohol to wash out the substance. This method is proposed by Enka Glanzstoff AG of Germany. However, glycerol contained within the wall of the capillary fibers is also dissolved out and removed. When glycerol has thus been removed, the capability of dialyzation of the dialyzer decreases considerably, even if a drying treatment has been applied to the capillary fibers afterwards. For this reason, it has hitherto been practiced to add glycerol afterwards once more to plasticize the fibers, washing thereafter the fibers with an organic solvent having water content of 70% or smaller to remove the glycerol adhered on the fiber wall, before the fibers are dried. Thus, in this case, a greater number of steps are required as indicated above. Also, the drying requires a longer period of time. Further, water, glycerol and the like will be contained in the organic solvent. Therefore, it is necessary to conduct a distillation operation requiring a large quantity of energy in order to reuse the solvent. In addition, ethyl alcohol has a tendency to catch fire exhibiting a danger of explosion. Furthermore, since ethyl alcohol has a relatively higher surface tension, it cannot penetrate into the inside of the pores of the capillary fibers uniformly, so that a better wash out of whole of the bundle of fibers cannot be attained.